The SWITCH method of VPGL Language is a condition branch of data flow.
SWITCH takes 2 inputs, and has 2 outputs, but emit 1 output to output 0 or output 1. SWITCH starts on both arriving objects on input 0 and input 1. SWITCH passes through input 0 to output 0 if input 1 is not NIL (including T – logically true), otherwise (input 1 is NIL) passes through input 0 to output 1. In both case, nothing is emitted to another output.